perf: lazy-load folders on demand; remove queue from config endpoint

Two startup cost reductions:

1. Folder enumeration is moved from /api/system/configuration to a new
   GET /api/system/folders endpoint. The frontend fetches it only when
   the user focuses a folder input field, and caches the result for the
   session. On large directory trees this was a noticeable startup delay.

2. The queue array is removed from /api/system/configuration. The queue
   is already loaded separately via /api/history/live on mount; including
   it in the config response was a double-load that inflated the initial
   payload for users with large queues.

app/routes/api/system.py

@@ -30,7 +30,7 @@ DIAGNOSTICS_CACHE_TTL = 5.0
 @route("GET", "api/system/configuration", "system.configuration")
 async def system_config(queue: DownloadQueue, config: Config, encoder: Encoder) -> Response:
     """
-    Pause non-active downloads.
+    Get the system configuration.
 
     Args:
         queue (DownloadQueue): The download queue instance.
@@ -47,13 +47,33 @@ async def system_config(queue: DownloadQueue, config: Config, encoder: Encoder)
             "presets": Presets.get_instance().get_all(),
             "dl_fields": await DLFields.get_instance().get_all_serialized(),
             "paused": queue.is_paused(),
+            "history_count": await queue.done.get_total_count(),
+        },
+        status=web.HTTPOk.status_code,
+        dumps=encoder.encode,
+    )
+
+
+@route("GET", "api/system/folders", "system.folders")
+async def system_folders(config: Config, encoder: Encoder) -> Response:
+    """
+    Get the list of folders available for downloads.
+
+    Args:
+        config (Config): The config instance.
+        encoder (Encoder): The encoder instance.
+
+    Returns:
+        Response: The response object.
+
+    """
+    return web.json_response(
+        data={
             "folders": list_folders(
                 path=Path(config.download_path),
                 base=Path(config.download_path),
                 depth_limit=config.download_path_depth - 1,
             ),
-            "history_count": await queue.done.get_total_count(),
-            "queue": (await queue.get("queue"))["queue"],
         },
         status=web.HTTPOk.status_code,
         dumps=encoder.encode,

app/tests/test_system_routes.py

@@ -1,7 +1,7 @@
 import json
 from dataclasses import dataclass
 from pathlib import Path
-from unittest.mock import AsyncMock, patch
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 
@@ -9,7 +9,7 @@ from app.library.config import Config
 from app.library.cache import Cache
 from app.library.encoder import Encoder
 from app.library.UpdateChecker import UpdateChecker
-from app.routes.api.system import check_updates, system_diagnostics, system_limits
+from app.routes.api.system import check_updates, system_config, system_diagnostics, system_folders, system_limits
 
 
 @dataclass
@@ -395,3 +395,58 @@ class TestSystemDiagnosticsEndpoint:
             )
 
         assert check.status == "skip"
+
+
+class TestSystemFoldersEndpoint:
+    def setup_method(self):
+        Config._reset_singleton()
+
+    @pytest.mark.asyncio
+    async def test_system_folders_returns_folder_list(self, tmp_path: Path) -> None:
+        """GET /api/system/folders returns the folders list."""
+        config = Config.get_instance()
+        config.download_path = str(tmp_path)
+        config.download_path_depth = 1
+        encoder = Encoder()
+
+        response = await system_folders(config, encoder)
+
+        assert response.status == 200
+        data = json.loads(response.body.decode("utf-8"))
+        assert "folders" in data
+        assert isinstance(data["folders"], list)
+
+
+class TestSystemConfigEndpoint:
+    def setup_method(self):
+        Config._reset_singleton()
+
+    @pytest.mark.asyncio
+    async def test_system_configuration_excludes_queue_and_folders(self, tmp_path: Path) -> None:
+        """GET /api/system/configuration no longer includes queue or folders."""
+        config = Config.get_instance()
+        config.download_path = str(tmp_path)
+        config.download_path_depth = 1
+        encoder = Encoder()
+
+        done_mock = MagicMock()
+        done_mock.get_total_count = AsyncMock(return_value=0)
+        queue = DummyQueue()
+        queue.done = done_mock
+
+        with patch("app.features.dl_fields.service.DLFields.get_instance") as mock_dlfields, \
+             patch("app.features.presets.service.Presets.get_instance") as mock_presets:
+            mock_dlfields_instance = MagicMock()
+            mock_dlfields_instance.get_all_serialized = AsyncMock(return_value=[])
+            mock_dlfields.return_value = mock_dlfields_instance
+
+            mock_presets_instance = MagicMock()
+            mock_presets_instance.get_all.return_value = []
+            mock_presets.return_value = mock_presets_instance
+
+            response = await system_config(queue, config, encoder)
+
+        assert response.status == 200
+        data = json.loads(response.body.decode("utf-8"))
+        assert "queue" not in data, "queue should be removed from config response"
+        assert "folders" not in data, "folders should be moved to /api/system/folders"

ui/app/components/NewDownload.vue

@@ -151,6 +151,7 @@
                     class="w-full"
                     size="lg"
                     :ui="{ root: 'w-full', base: 'bg-default/90' }"
+                    @focus="config.loadFolders()"
                   />
                 </div>
               </UFormField>

ui/app/components/PresetForm.vue

@@ -166,6 +166,7 @@
             :disabled="addInProgress"
             class="w-full"
             :ui="inputUi"
+            @focus="config.loadFolders()"
           />
         </div>
       </UFormField>

ui/app/components/TaskForm.vue

@@ -300,6 +300,7 @@
                 size="lg"
                 class="w-full"
                 :ui="inputUi"
+                @focus="config.loadFolders()"
               />
             </div>
           </UFormField>

ui/app/composables/useYtpConfig.ts

@@ -9,6 +9,7 @@ import { request } from '~/utils';
 
 let last_reload = 0;
 const CONFIG_TTL = 10;
+let isLoadingFolders = false;
 
 const state = reactive<ConfigState>({
   showForm: useStorage('showForm', true),
@@ -205,6 +206,23 @@ const patch = (feature: ConfigFeature, action: ConfigUpdateAction, data: unknown
   }
 };
 
+const loadFolders = async (): Promise<void> => {
+  if (state.folders.length > 0 || isLoadingFolders) return;
+  isLoadingFolders = true;
+  try {
+    const resp = await request('/api/system/folders', { timeout: 10 });
+    if (!resp.ok) {
+      return;
+    }
+    const data = await resp.json();
+    state.folders = data.folders ?? [];
+  } catch (e: any) {
+    console.error(`Failed to load folders: ${e}`);
+  } finally {
+    isLoadingFolders = false;
+  }
+};
+
 const ytpConfigApi = proxyRefs({
   ...toRefs(state),
   add,
@@ -215,6 +233,7 @@ const ytpConfigApi = proxyRefs({
   isLoaded,
   patch,
   loadConfig,
+  loadFolders,
 });
 
 export const useYtpConfig = () => ytpConfigApi;